Conventionally, a structure, which is approximate to the structure of human fingers, is adopted for a robot hand, and it is tried to grip a variety of objects. For example, a structure described in Patent Literature 1 is disclosed as a hand structure for stably gripping not only large objects but also small objects. The hand structure is provided with a plurality of finger mechanisms which correspond to a plurality of fingers. Each of the plurality of finger mechanisms is composed of a plurality of phalange sections including a distal phalange section and a middle phalange section which adjoins the distal phalange section. Then, the distal phalange section is made rotatable within a predetermined angle range in two directions of the inner direction and the outer direction as starting from a state in which the distal phalange section is stretched in a straight form with respect to the middle phalange section. Thus, an action is realized, which is approximate to the “pinching” action performed by human fingers.
On the other hand, another hand structure, which is described in Patent Literature 2, is accompanied by a link mechanism, and a finger is formed by a plurality of members. Further, in the case of this hand structure, when the rotation of the member disposed at the root of the finger is inhibited on account of the contact with an object, then another member is rotated with respect to the member disposed at the root, and thus an action is realized by the entire finger to enfold or roll up the object so that the gripping of the object is performed.
Further, Patent Literature 3 discloses such a construction that a base section is composed of a plurality of structural members, and the plurality of structural members are rotatably connected to one another by the aid of support portions, wherein the attraction is effected by a magnet to cause fixation, and an elastic member urges in a direction in which the structural members are separated from each other. In the case of this construction, if any external force is applied when the robot hand grips a gripping object, then the finger is separated from the structure of the hand at the root portion of the finger, by adjusting the relationship between the attractive force of the magnet and the urging force of the elastic member. Accordingly, it is possible to avoid such a situation that the finger and/or the gripping object is/are damaged by the applied external force.